Temperature-dependent polymorphic crystallization of poly(l-lactide)s on the basis of optical purity and microstructure

Song, Ping; Sang, Lin; Jin, Chenhao; Wei, Zhiyong

doi:10.1016/j.polymer.2017.11.069

Cited by 27 publications

(18 citation statements)

References 70 publications

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“…Growth rates are small at low and large undercooling, respectively, due to increased critical nucleus size in the first case and increased viscosity inhibiting segmental diffusion in the latter case. The obtained growth rate curve is in good agreement with previous works, which applied POM only or SALS and POM for different temperature intervals . Note that the present SALS experiment for the first time covered the entire temperature range of T c including the branch with low undercooling.…”

Section: Spherulite Linear Radial Growth Ratessupporting

confidence: 91%

“…A polymorphous α ′ / α ‐phase transition due to a change in chain packing during melt‐recrystallization, which depends on the thermal history and enantiomeric composition of the polymer, adds to the complexity of the melting behavior of polylactide. DSC experiments on this transition report a weak exothermic peak . SAXS experiments revealed a stronger increase of the difference in electron density between crystals and amorphous domains for the α ′ / α ‐phase transition than for a melt‐recrystallization of α ‐phase domains .…”

Section: Introductionmentioning

confidence: 92%

“…Comparison of Figure A,B and Figures S8 and S9 of the Supporting Information shows an amplification of the exothermic recrystallization peak as the crystallization temperature decreases from 110 to 80 °C, fully in line with the accompanying increase of the tendency to form α ′ ‐crystals. Recent studies demonstrated that the upper limiting temperature for the growth of α ′ ‐crystals shows a strong dependence on isomer composition of polylactide . While in case of enantio‐pure homopolymers the growth of α ′ ‐crystals is observed up to temperatures of 120 °C, α ′ ‐growth ceases already at a temperature of 90 °C in case of a random copolymer with a fraction of 4% of the minor repeat unit .…”

Section: Morphological Changes Upon Heating From the Crystalline Statementioning

confidence: 99%

“…SAXS experiments revealed a stronger increase of the difference in electron density between crystals and amorphous domains for the α ′ / α ‐phase transition than for a melt‐recrystallization of α ‐phase domains . An increase of D ‐lactide monomer content lowered the maximum temperature where an α ′ ‐phase is still formed during isothermal crystallization . WAXS experiments showed an isosbestic point for the 116 and 203 reflections during melt recrystallization .…”

Section: Introductionmentioning

confidence: 96%

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Phase Transformation Behavior of Polylactide Probed by Small Angle Light Scattering and Calorimetry

Schmidt

Keuker‐Baumann

Meyer

et al. 2019

J Polym Sci B Polym Phys

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Small angle light scattering (SALS) and differential scanning calorimetry DSC have been applied to investigate the melting of spherulites isothermally crystallized polylactide. At an isothermal crystallization temperature high enough, pure α-phase crystals are formed. Exposed to a temperature gradient, the crystals first melt and then recrystallize before they finally melt. With decreasing crystallization temperature, an increasing fraction of polylactide is crystallizing in the less stable α 0 -phase.α 0 -crystals also melt upon increasing the temperature but recrystallize to the more stable α-phase. A constant spherulite size is revealed by SALS for both processes, the α/α and α 0 /α meltrecrystallization, until completion of the final melting, thereby supporting integrity of the spherulites throughout the entire processes. Joint DSC and SALS experiments demonstrate that the depolarized scattering invariant correlates with the heat flow recorded by DSC and thus offer an alternative measure for the degree of crystallinity. The following mechanism is identified for both processes: initial melting and recrystallization overlay each other. Crystallinity is not fully recovered upon recrystallization because only part of the original lamellae survives the melt-recrystallization, though with an increased thickness. While lamellae are melting and reforming or simply transforming their phase, the spherulites survive the process until final melting.

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Section: Spherulite Linear Radial Growth Ratessupporting

confidence: 91%

Section: Introductionmentioning

confidence: 92%

Section: Morphological Changes Upon Heating From the Crystalline Statementioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

See 2 more Smart Citations

Phase Transformation Behavior of Polylactide Probed by Small Angle Light Scattering and Calorimetry

Schmidt

Keuker‐Baumann

Meyer

et al. 2019

J Polym Sci B Polym Phys

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show abstract

“…However, the effects of copolymerization on the formation of α ‐form and α ′‐(or δ ‐)form are rarely investigated. The only exception is that reported by Song et al for l ‐lactide‐rich poly( l ‐lactide‐ co ‐ d ‐lactide) copolymers whose [ T c ( α ‐ δ )] decreased slowly with decreasing l ‐lactide unit content …”

Section: Introductionmentioning

confidence: 85%

Stereocomplex crystallization, homocrystallization, and polymorphism of enantiomeric copolyesteramides poly(lactic acid‐ co ‐alanine)s from the melt

Tsuji

Sato

Masaki

et al. 2019

Polymer Crystallization

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Stereocomplex (SC) crystallization, homocrystallization, and polymorphism of poly(Llactic acid-co-L-alanine) [P(LLA-LAL)] and poly(D-lactic acid-co-D-alanine) [P(DLA-DAL)] copolymers with wide alanine unit content ranges from 0 to 21 and 22 mol% are investigated for melt-crystallization. P(LLA-LAL)/P(DLA-DAL) blends crystallize for wide alanine unit content ranges compared to unblended P(LLA-LAL) and P(DLA-DAL) samples, due to facile SC crystallization compared to homocrystallization. The phase diagrams of the unblended samples [α-and δ-form homocrystallites] and the blend samples (SC and homocrystallites) are drawn. The transition crystallization temperature of unblended samples from α-form to δ-form decreases with an increase in alanine unit content. In the unblended and blend samples, alanine units are correspondingly incorporated in α-form homocrystalline regions and excluded from SC crystalline regions. The maximum radial growth rate values of spherulites are higher for the blend samples than for the unblended samples. The experimental crystallization half time [t c (1/2)(exp)] values of the unblended samples increase with an increase in alanine unit content, whereas the t c (1/2)(exp) values of the blend samples with alanine unit contents of 3 and 4 mol% and 6 and 6 mol% and of 12 and 13 mol % are respectively higher than and similar to those of poly(L-lactic acid)/poly(D-lactic acid) blend.

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Effect of the configuration of poly(lactic acid) and content of poly(oxyethylene) blocks to the structure and functional properties of poly(lactic acid)‐block‐poly(oxirane)‐based nanofibrous electrospun polyester–ether–urethanes used as potential drug‐delivery system

et al. 2019

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Poly(lactic acid)‐block‐poly(oxirane)s (PLA‐b‐POE) of various compositions were prepared using a one‐pot approach and then extended in a reaction with l‐lysine diethyl ester diisocyanate, thereby forming polyester–ether–urethanes (PEU) with prolonged chains and units with increased degradability. The PEUs are processed by electrospinning to prepare degradable nanofibrous sheet materials with and without encapsulating the antibiotic Vancomycin (VAC). PLA block isomerism and POE blocks oligomeric content (1000 g/mol) affect the thermal properties, processability, nanofibrous sheet morphology, abiotic degradation, cytocompatibility, and encapsulated antibiotic release rate of prepared PEUs. Therefore, our findings provide an effective approach to tuning the functional properties of these advanced biocompatible materials. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2378–2387, 2019.

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Temperature-dependent polymorphic crystallization of poly(l-lactide)s on the basis of optical purity and microstructure

Cited by 27 publications

References 70 publications

Phase Transformation Behavior of Polylactide Probed by Small Angle Light Scattering and Calorimetry

Phase Transformation Behavior of Polylactide Probed by Small Angle Light Scattering and Calorimetry

Stereocomplex crystallization, homocrystallization, and polymorphism of enantiomeric copolyesteramides poly(lactic acid‐ co ‐alanine)s from the melt

Effect of the configuration of poly(lactic acid) and content of poly(oxyethylene) blocks to the structure and functional properties of poly(lactic acid)‐block‐poly(oxirane)‐based nanofibrous electrospun polyester–ether–urethanes used as potential drug‐delivery system

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